Role of Microstructure in Oxygen Induced Photodegradation of Methylammonium Lead Triiodide Perovskite Films

Abstract

photovoltaic technology, where lifetimes greater than 25 years are required. [2] Although the issue of device stability has attracted increased attention of the photovoltaic research community in the last two years, reports that systematically study the fundamental causes (e.g., heat, electrical stress, humidity, oxygen, (UV) light, chemical precursors, processing conditions, influence of film quality and morphology) and mechanisms limiting the material and device stability remain scarce. [2][3][4][5] While the degradation of methylammonium lead iodide (MAPbI 3 ) in humid air has been studied experimentally as well as theoretically and was long thought to be the main factor for material degradation in ambient environment, [6][7][8][9][10][11][12][13][14][15] studies exploring the influence of oxygen and light on the solar cell performance have only recently been reported. [16][17][18][19][20] It has been shown that photoexcited electrons in the perovskite layer can form superoxide (O 2 − ) via electron transfer to molecular oxygen, which through deprotonation of the methylammonium cation in turn results in irreversible material degradation. The severity of the degradation has been linked to the efficiency of electron extraction via the electron extracting layer (EEL): devices employing a compact-TiO 2 /mesoporous Al 2 O 3 or compact-TiO 2 as EELs degraded in dry air on a timescale of less than 1 h, while with the use of a mesoporous TiO 2 layer, an EEL which results in faster electron extraction, the lifetimes were significantly increased. However, in these reports only the degradation of complete photovoltaic device was reported, with limited information on the degradation of the perovskite active layer itself and the impact of its microstructure was not identified.In this work, we systematically study the degradation of MAPbI 3 films under precisely controlled exposure to various oxygen levels (0-20%) under simulated sunlight in order to shed light on the progression of perovskite degradation under these conditions. We investigate two types of perovskite layers that are formed using different fabrication methods. The two recipes allow us to include the effect of layer microstructure on the dynamics of oxygen-induced degradation. We characterize the electronic, optical, compositional, and structural properties of the degraded perovskite films and correlate these results This paper investigates the impact of microstructure on the degradation rate of methylammonium lead triiodide (MAPbI 3 ) perovskite films upon exposure to light and oxygen. By comparing the oxygen induced degradation of perovskite films of different microstructure-fabricated using either a lead acetate trihydrate precursor or a solvent engineering technique-it is demonstrated that films with larger and more uniform grains and better electronic quality show a significantly reduced degradation compared to films with smaller, more irregular grains. The effect of degradation on the optical, compositional, and microstructural properties of the perovsk...

Role of Water and Defects in Photo‐Oxidative Degradation of Methylammonium Lead Iodide Perovskite

“…Specifically, the influence of oxygen and light on MAPbI 3 has attracted great attention recently, and the study on improving the stability of MAPbI 3 against photo‐oxidation is springing up . Zhang and Sit have reported a pathway for breaking of the local octahedral Pb–I structure and the formation of the PbO precursor .…”

Exploring Red, Green, and Blue Light‐Activated Degradation of Perovskite Films and Solar Cells for Near Space Applications

“…It is found that heat destroys the perovskite film in a layer‐by‐layer pathway sequentially from the surface to bulk with a lattice transition, causing a dramatic loss in photovoltaic performance . Oxygen could act as a catalyst to prompt CH 3 NH 3 + disintegrating into CH 3 NH 2 and hydrogen under irradiation . The perovskite semiconductor is sensitive to atmospheric environment.…”

The Gold(I)‐Mediated Domino Reaction to Fused Diphenyl Phosphoniumfluorenes: Mechanistic Consequences for Gold‐Catalyzed Hydroarylations and Application in Solar Cells

“…Inverted architecture perovskite solar cell means that in this architecture indium tin oxide (ITO) is the anode, whereas the metal contact constitutes the cathode. Devices with 3 c –H were compared to devices without a HBL and with the commonly used bathocuproine (BCP) . Summarizing the results of CV, UV/Vis spectroscopy, and the ultraviolet photoemission spectroscopy (UPS) measurements, the corresponding energy diagram is shown in Figure b.…”

“…PEDOT:PSS was spin coated on the cleaned ITO substrate with annealing at 150 °C for 15 min. Lead acetate trihydrate perovskite solution was spin coated onto PEDOT:PSS in a drybox (relative humidity <5 %) with drying for 5 min and annealing at 100 °C for 5 min . The prepared samples were transferred into a N 2 ‐filled glovebox.…”